1. Field of the Invention
The present invention relates to a transparent conductive film for use in a display device, and more particularly, to a method of varying a transmittance of a transparent conductive film. The present invention further relates to a flat panel display and a manufacturing method thereof.
2. Description of the Related Art
A transparent conductive film has an excellent transmittance of more than 80% and a high conductivity, and is used as, for example, a pixel electrode or a common electrode of a solar battery or a display device, such as a plasma display panel (PDP), a liquid crystal display (LCD), and an organic light emitting diode (OLED). The transparent conductive film plays a very important role in transmitting light to reproduce a color.
FIG. 1 shows a cross-sectional view illustrating a conventional organic electroluminescent (EL) display device having a transparent conductive film as a pixel electrode.
An insulating substrate 500 having first and second regions 501 and 502 is provided. A pixel will be formed on the first region 501, and a thin film transistor (TFT) and a storage capacitor will be formed on the second region 502.
A buffer layer 520 is formed on the insulating substrate 500. A semiconductor layer 530 is formed on a portion of the buffer layer 520 over the second region 502. A gate insulating layer 540 is formed over the entire surface of the substrate 500. A gate electrode 551 is formed on a portion of the gate insulating layer 540 over the semiconductor layer 530. A lower capacitor electrode 552 is formed at the same time as the gate electrode 551.
An n-type impurity or a p-type impurity is ion-doped to form source and drain regions 531 and 532. A portion 533 of the semiconductor layer 530 between the source and drain regions 531 and 532 serves as a channel region.
An interlayer insulating layer 560 is formed over the entire surface of the substrate 500. The gate insulating layer 540 and the interlayer insulating layer 560 are simultaneously etched to expose portions of the source and drain regions 531 and 532, thereby forming contact holes 561 and 562.
Next, source and drain electrodes 571 and 572 are formed on the interlayer insulating layer 560 to contact the source and drain regions 531 and 532, respectively. At the same time, an upper capacitor electrode 573 is formed to connect either of the source and drain electrodes 571 and 572. In FIG. 1, the upper capacitor electrode 573 is connected to the source electrode 571. A portion of the interlayer insulating layer 560 formed over the lower capacitor electrode 522 serves as a dielectric layer of the capacitor.
Subsequently, a passivation film 580 is formed on the interlayer insulating layer 560. The passivation film 580 is etched to expose either of the source and drain electrodes 571 and 572, thereby forming a via hole 581. In FIG. 1, the via hole 581 exposes a portion of the drain electrode 572.
Thereafter, a transparent conductive film made of, e.g., indium tin oxide (ITO) is deposited on the passivation film 580 and patterned to thereby form a pixel electrode 590 (i.e., anode electrode) over the first region 501. The pixel electrode 590 is electrically connected to the drain electrode 572 through the via hole 581.
Subsequently, a planarization layer 600 is formed over the entire surface of the substrate 500, and is patterned to form an opening portion 610. The opening portion 610 exposes a portion of the anode electrode 590.
An organic EL layer 620 is formed on the exposed portion of the anode electrode 590. A cathode electrode 630 is formed to cover the organic EL layer 620, thereby completing the conventional organic EL display device.
A flat panel display device such as an active matrix organic EL display device described above includes a switching element and wire lines which are used to apply electrical power to the switching element. Ambient light is reflected from the wire lines made of a metal, and thus a contrast ratio is lowered. In other words, the ambient light is reflected from the lower and upper capacitor electrodes, the source and drain electrodes and the cathode electrode.
A polarizer can be arranged to prevent the contrast ratio from being lowered. However, the cost of incorporating the polarizer is high, increasing the overall manufacturing cost of the organic EL display device. In addition, the polarizer shields light emitted from the organic EL layer 620 and thus lowers a transmittance, leading to a low brightness.
Alternatively, a black matrix made of Cr/CrOx or an organic material can be formed over the rest of the second region 502 except for the first region 501 to prevent the contrast ratio from being lowered. However, this requires an additional mask process to form the black matrix. In addition, with an increase (deepening) of a step difference between the first and second regions 501 and 502, a short circuit between the gate electrode 551 and the source and drain electrodes 531 and 532 may occur.